The present invention relates generally to trace gas detection and more specifically to laser absorption spectroscopy systems and methods.
Optical absorption spectroscopy involves passing radiation through a sample, e.g., an analyte and measuring absorption property of the sample as a function of the radiation wavelength. For example, trace gas detection can be spectroscopically performed by taking measurements to detect the presence or absence of spectral absorption lines corresponding to the gas species of interest. Trace gas detection can be spectroscopically performed by taking measurements to quantify spectral absorption lines corresponding to the gas species of interest and to compute concentrations of analytes, gas pressure, and gas temperature. Spectroscopic analysis of isotopologues can also be performed. However, because the integral line intensities of absorption gas lines are sensitive to the gas temperature, and the line shapes of those lines are sensitive to the gas temperature, the gas pressure, and the gas composition, measurements of the isotopic ratio with high accuracy require highly accurate measurements of the analyzed gas temperature and pressure. In addition, such measurements of the integral intensities of different lines also require very precise measurements of laser frequency. Moreover, because the natural abundance for isotopes can be very different, the integral line intensities of absorption gas lines of different isotopologues can also be very different, because the integral intensities are the products of the line strengths, gas concentration and isotpologue abundance. That is why it might be hard to precisely measure the integral intensities of the absorption lines of less abundant isotopologues and as a result of that to precisely measure the ratio of concentrations of two isotopologues with quite different abundances.
Accordingly it is desirable to provide improved spectroscopy systems and methods for measuring concentrations of different isotopologues in their gas phase.